Method for producing steel sheets or strips for making cans

ABSTRACT

1. A METHOD FOR PRODUCING CAN-MAKING STEEL SHEET COMPRISING SUBJECTING A STEEL SLAB CONTAINING NOT MORE THAN 0.03% C, NOT MORE THAN 1.0% MN, NOT MORE THAN 0.04% P, NOT MORE THAN 0.02% O, WITH THE BALANCE BEING IRON AND UNAVOIDABLE IMPURITIES TO FINISH HOT ROLLING AT A TEMPERTURE BETWEEN THE A3 TRANSFORMATION POINT AND 750* C., COILING THE SHEET AT A TEMPERATURE NOT LOWER THAN 620*C., AND COLD ROLLING THUS OBTAINED HOT ROLLED SHEET OR STRIP AFTER ACID PICKLING WITH A REDUCTION RATE NOT LOWER THAN 80%.

United States Patent 3,843,423 METHOD FOR PRODUCING STEEL SHEETS OR STRIPS FOR MAKING CANS Hidejiro Asano, Kitakyushu, and Yashichi Oyagl,

Yachiyo-machi, Japan, assignors to Nippon Steel Corporation, Tokyo, Japan No Drawing. Filed Aug. 23, 1973, Ser. No. 391,020 Claims priority, application Japan, Aug. 24, 1972, 47/ 84,100 Int. Cl. C21d 9/46 US. Cl. 148-12 1 Claim ABSTRACT OF THE DISCLOSURE The present invention relates to a very economical method for producing steel sheets for can-making.

More particularly, the present invention is to provide an economical method for producing steel sheets or strips (herein after called sheets) for can-making, having satisfactory workability (can-making properties) similar or better than those of the can-making steel sheet (so-called twice cold rolled sheet abridged as 2 C R steel sheet) obtained by cold rolling annealed cold rolled sheet again and by metal coating the sheet, or those of the can-making steel sheet obtained by stress-relief annealing a cold rolled steel sheet.

As widely known, very extensive studies have been made for a method for producing low-cost can-making steel sheets in the steel making industry and various proposals have been made up to now. The problem which is most concerned at the present time is to provide steel sheets having satisfactory can-making properties at low cost, and already at the present time some methods have been known for producing relatively low cost can-making steel sheets.

For example, Progress on Metal Containers, K. W. Brighton, Canned Foods, page 3 and a Japanese Patent Publication Sho 38-85 63 disclose a method for producing can-making steel sheets by two-step cold rolling, and Japanese patent publications Sho 41-18486 and Sho 43- 12504 disclose a method for producing can-making steel sheets by annealing the sheet at a low temperature for incomplete recrystallization after cold rolling.

However, according to thetwo-step cold rolling methods disclosed in the above first two prior publications, it is necessary to conduct the first-step cold rolling and annealing and in addition the second-step cold rolling, and according to the methods disclosed in the latter two prior publications, the sheet after the cold rolling is annealed at a low temperature. Although the products produced by the above conventional methods have high strength and good can-making properties, it is necessary in the former method to conduct the additional cold rolling, thus causing disadvantages in respect of equipments and necessity of use of high cost rolling oil as well as provision of a subsequent degreasing line, and the latter method, although advantageous over the former method, has disadvantages in respect of the annealing time and production cost due to the low temperature annealing of cold rolled steel sheets. a

The conventional two-step method for producing canmaking steel sheets includes steps of hot rollingacid picklingcold rolling-electrolytic degreasing-annealing-second cold rolling-electrolytic degreasing-plating, while the low temperature annealing method includes steps of hot rollingacid picklingcold rollingelectrolytic degreasing--stress-relief annealing-shape correcting (may be omitted)planting. According to the conventional methods, complete annealing is conducted at a temperature higher than 600 C. in order to remove the work hardening effect of the cold rolled steel sheets or stress-relief annealing is conducted at a temperature between 400 and 600 C.

It is clear that if such annealing steps can be omitted, very economical production of can-making steel sheet is possible.

The present invention is based on the above facts and has been completed as a result of extensive studies for obtaining good can-making properties by combination of steel composition and operational conditions of production steps without an annealing step.

The gist of the present invention lies in the method for producing can-making steel sheets which is characterized in that a steel slab containing not more than 0.03% C, not more than 1.0% Mn, not more than 0.04% P, not more than 0.02% O with the balance being iron and unavoidable impurities is subjected to finishing rolling in a temperature range from its A transformation point to 750 C., coiled at a temperature not lower than 620 C. and thus obtained hot rolled steel sheet is acid pickled and cold rolled with a reduction rate not lower than More particularly, steel ingot or slab containing not more than 0.03% C, not more than 1.0% Mn, not more than 0.04% P, not more than 0.02% O with the balance being iron and unavoidable impurities is prepared by the conventional mold casting method or continuous casting method, and the slab which produced above method is heated to 1000 to 1300 C. in slab reheating furnace and hot rolled.

In the hot rolling, the temperature when the sheet passes the final rolling rolls, namely the finishing outlet temperature and the coiling temperature are important. According to the present invention, the temperature at the hot rolling finishing outlet should be between the A transformation point of the steel and 750 C. and the coiling temperature should be not less than 620 C. for the reasons herein set forth.

The hot rolled coil thus obtained is acid pickled and cold rolled at a reduction rate not less than 80% into cold rolled strip of 0.1 to 0.5 mm. thickness. This cold rolled strip is directly used as can-making cold rolled steel sheet, and no subsequent annealing for the purpose of stress relief is required.

The reasons for the above limitations in the present invention will be explained hereinunder.

The carbon content is limited to not more than 0.03% for the following reason. It has been conventionally considered that when work strain remains in steel sheet, corrosion resistance is deteriorated, but it has been found by the present inventors that corrosion resistance is remarkably improved by lowering the carbon content to not more than 0.03%, preferably 0.018%, and that some carbon content is necessary for obtaining strength required by cans. Manganese is added to prevent lowering of hot workability of hot rolled sheet due to sulfur and to give the sheet required strength. However, the manganese content should be not more than 1.0%, but in an amount more than three times of the sulfur content. Phosphorus should be not more than 0.04% because it remarkably deteriorates corrosion resistance of the steel sheet. Oxygen is a harmful element, because it combines with manganese and silicon in the steel to form oxides, thus lowering cleanness of the steel and deteriorating can-making properties. Particularly high degree of cleanness of the steel is required when cold rolling of more than 80% reduction rate is done as in the present invention. Thus, the oxygen of the hot rolling does not exceed the A transformation point of the steel and the sheet is coiled at a temperature not lower than 620 C. The coiled steel strip is maintained at the temperature for substantial time so that the steel is subjected to recrystallization annealing by its own content is limited to not more than 0.02%. Among the 5 heat and the hot rolled structure is eliminated. When the hot rolling conditions, the finish ng rolling temperature soft hot rolled steel sheet thus produced is subjected to and the corlmg temperature areimportant for obtaining cold rolling of more than 80% reduction according to excellent strength and workability for can-making, parthe present invention, tensile strength of the sheet as cold ticularly n case of cold rolled steel sheets which have rolled will be lower than about 70 kg./mm. and it is posbeen sub ected to strong cold reduction. The reason for sible to improve the productivity of cans without sacrifice defining the fin shmgrolhng temperature as between the of can-making properties. A transformation point and 750 is that this tempera- For the actual practice of the present invention, steel ture range is optimum for formation of complete equicontaining not more than 0.03% C, not more than 1.0% axed grains free from hot rolled structure, and the reason Mn, not more than 0.04% P, not more than 0.02% O for odefinlng coiling temperaturefis f lower than with the balance being iron and unavoidable impurities 62:0 C. that this temperature range is desirable for 0bis prepared in an ordinary steel making furnace such as 9 3 g L 3 of i sheet for can'makmg and a converter, an open hearth, and an electric furnace. Vac- IS eslra 6 mm e Pomt 0 ecolflomyfi uum degassing may be used to adjust the carbon and oxy- The advantage of the present invention is that satist t factory workability of the sheet for can-making can be gen con en d obtained only by the strong cold rolling of more than 80% Thus prePared molten. Steel ma e Slabs by (ionreduction rate through the combination of the steel comtmuous castmg or an oldmary mgot'makmg and breikmg' position and the production conditions, and that satisfacw j and sublecfed to the t of hot mungtory mechanical properties for maintaining require can- Field Picklmg co1d roumgdegreasmg shape correct strength can be obt ined, mg (may be omitted)-plating to obtain the final product.

Can-making properties of can-making steel sheets pro- In the Plating p, fill-Plating, Chromium-Plating chemduced by the conventional methods as described hereini681 Conversion treatment is effectedbefore from steel of the ladle analysis shown in Table 1 The present invention will be more clearly understood are good. from the following examples.

TABLE 1 Percent of- 0 Si M11 P S Cu N act-0.15---- 0.0s 0. 20-0. 70 0.01-0.14 0. (us-0.050 0. 02-0. 20 0. 001-0. 025

However, the can-making steel stocks produced by the EXAMPLE 1 conventional methods require annealing and workability of the sheet as cold rolled with heavy reduction is poor Steel having the composition shown in Table 2 was and it is impossible to work the sheet into cans directly. prepared in a converter and part of the molten steel was According to the present invention, excellent can-maksubjected to vacuum degassing to adjust the composition. ing properties :an be given to the cold rolled steel sheet These steels were hot rolled With the finishing outlet temobtained by strong cold rolling of more than 80% reducperature at a temperature not higher than the A transfortion rate thanks to the steel composition as specified mation point, namely between 780 and 840 C- (aiming at above, and no annealing is required after the cold rolling due to the lowered carbon and oxygen contents. In this point, the present invention is essentially difierent from 810 C.), and were coiled at 640 C. Thus obtained hot rolled sheets were cold rolled with a reduction rate of 89% into cold rolled steel sheets of 0.26 mm. thickness.

TABLE 2 Mn P S CU. Al O N 0. 36 0. 017 0. 016 0. 03 tr. 0. 042 0. 0026 0. 49 0. 016 0. 012 0. 03 0. 051 O. 008 0. 0059 0. 28 0. 010 O. 021 0. 05 0. 004 0. 035 0. 0061 0. 25 0. 060 0. 012 0. 04 0. 038 0. 014 0. 0038 0. 4.1 0. 008 0. 010 0. 02 0. 010 0. 007 0. 0041 0. 33 0. 014 0. 024 0. 03 0. 072 0. 006 0. 0040 0. 27 0. 010 0. 019 0. 13 0. 042 0. 010 0. 0051 0. 48 0. 026 0. 014 0. 02 0. 031 0. 009 0. 0068 Norm-No. 1 to No. 4 are outside the steel composition of the present invention. No. 5 to No. 8 are within the steel composition of the present invention.

the conventional methods for producing can-making steel sheets. On the other hand, if the steel composition of the present invention is subjected to the finishing outlet temperature of higher than the A transformation point as in the conventional methods, only can-making steel sheet of excessively high strength is obtained, although enough can-making properties are obtained. Such excessively high strength of the can-making steel sheet necessarily causes difficulties in respect of rigidity of the can-making machine and the driving source, and is not always desirable even when satisfactory can-making properties can be obtained. Rather, can-making steel sheets having lower strength as cold rolled condition are increasingly demanded in more and more cases in recent years. In order to obtain tensile strength of not more than about kg./rnm. as cold rolled with more than 80% reduction rate, it is necessary that the finishing outlet temperature Table 3 shows the mechanical properties and workability into beer can lids as well as can-making feasibility 60 of the cold rolled steel sheets thus obtained.

NOTE: (1) Can-making workability is shown by the workability into beer can lids; (2) Can-making feasibility was determined by occurence of cans of poor seaming in the seaming step after the beer can hd stamping step; (3) No. 1-No. 4 are cold rolled sheets from the steels of No. 1 to No. 4 in Table 2, and No. 5 to N0. 8 are cold rolled sheets from the steels of N0. 5 to No. 8 in Table 2; (4) 0=good, X=had.

No. l to No. 4 which are outside the composition of the present invention (No. 1 is outside the composition in respect of C and O, No. 2 in respect of C, No. 3 in respect of O, and No. 4 in respect of P) could not be worked into cans or had poor can-making feasibility even when they had some workability. On the other hand, No. 4 to No. 8, which are within the composition of the present invention, were excellent both in can-making workability and can-making feasibility.

EXAMPLE 2 Steel having the composition shown in Table 4 was hot rolled under the conditions shown in Table 4 and cold rolled with reduction rate of 87% into cold rolled sheets of 0.27 mm. thickness, and their mechanical properties, workability, can-making feasibility are shown in Table 5. A in Table 5 indicates the finishing outlet temperature not lower than the A transformation point, and B represents the finishing outlet temperature not higher than the A transformation point. As clearly seen from the results shown in the table, the can-making feasibility of No. 3B which is within the composition of the present invention is poor due to the too low coiling temperature in spite of the finishing rolling temperature below the A transformation point. No. 4, due to its high carbon content, shows slightly lower can-making feasibility in spite of satisfactory hot rolling conditions. On the other hand, No. 1B and No. 2B which are within the scope of the present invention show remarkably excellent can-making feasibility in particular.

What is claimed: 1. A method for producing can-making steel sheet comprising subjecting a steel slab containing not more than 0.03% C, not more than 1.0% Mn, not more than 0.04% P, not more than 0.02% O, with the balance being iron and unavoidable impurities to finish hot rolling at a temerature between the A transformation point and 750 C., coiling the sheet at a temperature not lower than 620 C., and cold rolling thus obtained hot rolled sheet or strip after acid pickling with a reduction rate not lower than 80%.

TABLE4 Hot rolling condition Finish- Oomposltions (percent) ing Coiling temp. temp. Sample No; 0 Si Mn P S Cu Al 0 N A 905 1 -.{B 0.015 0. 021 0.34 0.009 0.016 0.03 0.001 0.009 0.0041 800 650 AIIIIIII 0. 920 2.---:.; {B 007 0. 011 0.29 0.014 0.008 0.02 0.063 0.007 0.0062 820 670 AIIIIII 915 3..':.':.'. {B 0.011 0.024 0. 46 0. 011 0.014 0.02 0.045 0.012 0.0045 815} 600 AIIIII'. 885 4.--.:.. {B }0.035 0.021 0.38 0.018 0.011 0.03 0.031 0.010 0.0039 805} 650 References Cited UNITED STATES PATENTS 2,814,578 11/1957 White 14812 3,264,144 8/ 1966 Frazier et a1. 148--12 3,614,886 10/1971 Nishihara 148--12 WAYLAND W. STALLARD, Primary Examiner 

1. A METHOD FOR PRODUCING CAN-MAKING STEEL SHEET COMPRISING SUBJECTING A STEEL SLAB CONTAINING NOT MORE THAN 0.03% C, NOT MORE THAN 1.0% MN, NOT MORE THAN 0.04% P, NOT MORE THAN 0.02% O, WITH THE BALANCE BEING IRON AND UNAVOIDABLE IMPURITIES TO FINISH HOT ROLLING AT A TEMPERTURE BETWEEN THE A3 TRANSFORMATION POINT AND 750* C., COILING THE SHEET AT A TEMPERATURE NOT LOWER THAN 620*C., AND COLD ROLLING THUS OBTAINED HOT ROLLED SHEET OR STRIP AFTER ACID PICKLING WITH A REDUCTION RATE NOT LOWER THAN 80%. 